Sadly, my umbee was killed by the red terror. He was about 5 inches long and was an extremely placid fish. The festae only attacked him because he wanted to hide in her spot. I still stand by my philosophy regarding fish aggression. I think it's reacton when people taunt their fish and they bite the glass. That terrifies them. They remember it. The act of aggression is taunting the fish to agitate him.
feeding lots of live food makes a monster out of monster fish. Live is good, but your fish don't need to eat mice.
Treat the fish with respect and give him a proper environment with ample territory and line of sight breakers.
I believe with my whole heart that it's the way many owners treat their fish [instigating the glass biting] that we have so many mean fish stories. Read the old literature. The dovii was described as a timid monster. The fish remember that and they know full well they are in a confined space. It frightens them. They are always on the defensive.
I have a 14 in jaguar cichlid and a shoal of 12 clown loaches, 4 of which are less than 4 inches long. They sleep right next to the jaguar, he never harms them. They aren't a threat to him, they aren't food to him.
Of course.....individual variation plays a part. you can't look at a bus full of people and say "are they all good or all evil?" I'm sure there are lots of outrageously aggressive fish no matter what you do. I just think it is/could be/should be lower than reported.